Purification of titanium tetrachloride



May 27, i958 c. K. sToDDARD Ef Ax.

PURFICATION OF TITANIUM TETRACHLORIDE Filed June 2l. 1954 AGENT United States Patent C PURIFrCArIoN or rrrANnn/i rnfrnacrnonmn Carl Ker-hy Stoddarf, Henderson, and Phillip J. Maddox,

Las Vegas, Nev., assignors to Titanium Metals Corporation of America, Pittsburgh, Pa., a corporation of Pennsylvania Application Enne 2l, 1954, Serial No. 437,914

6 Claims. (Cl. 22-57) This invention relates to the purification of titanium tetrachloride and more particularly to the treatment of crude titanium tetrachloride to produce purified material suitable for the manufacture of titanium metal.

Methods for purication of titanium tetrachloride to produce raw material for pigment production are well known. It has been necessary in order to produce proper quality pigment to insure that tetrachloride used for this purpose is water-white and contains no impurities which would harm the paint makingY or color characteristics of TiO2 manufactured from it. The problems involved in the manufacture of titanium metal, however, are different. impurities which apparently have no deleterious effect on pigment production have been found to render titanium tetrachloride unsuitable for the production of ductile titanium metal. The effect and permissible amounts of some of these impurities are not completely appreciated even at this time, however, it is known that phosgene, free chlorine and solid material which may contain oxidic compounds as well as vanadium salts, which are often present in titanium ores, are definitely harmful. lt has not been possible by heretofore known methods to treat titanium tetrachloride continuously and efiiciently to produce a raw material which will insure the production of ductile metal.

It is therefore the object of this invention to provide an improved method for the purification of titanium tetrachloride. Another object of this invention is to provide a method for producing purified titanium tetrachloride of a grade suitable for the production of ductile titanium metal. Still another object of this invention is to provide a continuous, efficient and economical method for the purification of titanium tetrachloride. Yet another object is to provide a method for purification of titanium tetrachloride which will separate harmful gaseous as well as solid and soluble impurities. This and other objects of this invention will be apparent from the following more detailed description thereof and from the annexed drawing which illustrates a general flow sheet of a preferred embodiment of the method of this invention.

Referring now to the drawing, the crude TiCl4 as it is transferred from the chlorinators is first subjected to a vaporization treatment. The vapors pass out of the vaporizer and are condensed, the residual solids being transferred to a sludge boiler for recovery of TiCl4 values as will be hereinafter described in more detail. The condensed TiCl., which at this stage will have been freed from non-volatile solid impurities is then treated with a chemical treating agent capable of precipitating soluble compounds such as vanadium salts. This chemical treating agent may preferably be H28 or any one of a number of compounds which have been proposed in the prior art, for instance, metallic copper, carbon, oils and organic compounds. It is preferred to vconduct the chemical treatment at elevated temperature and sufficient treating agent is added to insure as complete as possible precipitation of vanadium and like impurities. As a control,

ice

the TiCl4 at this stage may be analyzed for vanadium content, or a water-white color maybe taken as an indication of adequate treatment. After treatment, the treated TiClg is transferred to a second vaporizer to distill off the titanium tetrochloride from the precipitated solids. The vapors from the second vaporization stage are condensed and the residue from this operation is transferred to the sludge boiler.

The condensed and treated TiCl4 is then transferred to the first rectifying column which separates the low boiling impurities from the TiClg. The column is maintained in operation by provision of a boiler which vaporizes TiCl., at or near its base and the separated low boiling point impurities volatilized Aat the top of the column are refluxed and discarded. The TiCl.,L taken from the Vbottom of the column freed from low boiling point impurities is then passed to a secondrectifying column where high boiling point impurities are separated. This column is of the same general nature as the first rectifying column but operated so that purified TiCl4 will be drawn off at the top of the column and the high boiling point impurities will be taken from the bottom of the column. A boiler is provided to continuously vaporize TiCl for proper column operation. The purified TiCl4 product taken from the top of the second column is condensed and will be found of purity suitable for the manufacture of ductile metallic titanium. The high boiling point impurities taken from the bottom of the second rectifying column will feed back into the sludge boiler with a proportion thereof being separated and discarded.

The sludge boiler as noted above receives the residue material from the first vaporizer, the second vaporizer, and a proportion of the high boiling point impurities from the second rectifying column. Since all these materials will contain a substantial proportion of TiCl4, the sludge boiler is operated to separate TiCl4t from solids and otherv impurities. Operation is accomplished by a simple volatilization, the solid titanium residue being discarded and the TiCl,E vapors condensed, preferably, and then fed back into the first vaporizer. The flow sheet therefore, illustrates a complete integrated, continuous process for purifying TiCl4 with values recovered as far as possible from separated impurities. y f

The crude TiC14 as received from the chlorinators, a it enters the system described, may contain a number of harmful solid and gaseous impurities. These may include dust, finely divided particles of the chlorinator feed materials such as carbon and rutile -or ilmenite, iron compounds, vanadium compounds, free chlorine, phosgene, HC1, tin chloride, silicon chloride, zirconium chloride, chromium chlorides, as well as other impurities. The first vaporization step is not essential in the process and if desired the crude TiCl., may be transferred directly to the chemical treatment step. It is advantageous, however, to employ a preliminary vaporization in order to separate the solid impurities from the TiCl4 before chemical treatment. It has been found that a considerably increased amount of chemical treating agent is necessary to produce properly treated TiCl4 when the solid impurities are allowed to remain in the TiCl4. The first vaporizer is operated so that a major portion of the crude TiCl.,t is distilled over into the following condenser. It is not desirable at this stage to conduct the evaporation so as to produce a dry residue but better operating conditions will be obtained if a portion of TiCl4remains with the solid impurities so that a liquid slurry is produced in the still bottom which may be readily handled by ordinary transfer pipes and pumping equipment. It will be found convenient and advantageous to operate the first vaporization so that between 50 and 80%r of the TiCl4 content of the crude feed is evaporated and condensed.

The chemicaltreatment operation is conducted inY acl i cordance with'best practicek considering the amount of impurities precipitated and the nature of the chemical treating agent employed. I -IgS is av preferred treating agent andwhen-gthisjisiused, sutticientis added to the l`iCl4V to produceV a water-white product substantially free from vanadium compounds'.` In the chemical treatmenta substantial amount 'of precipitation `of impuri ties occurs, in addition vto coagulation of finely Ydivided suspended materialA .Therefore in order to `provide a con- N l kveniently handled still bottom material the second vapor-v iaation step like ,theY first is not carried'to Vthe point where the .following condense"r.. The residue material Y,which isiiuid by reason of the amount ofTiCl., still ypresent in admiXture with the solids lwill be found to be conveniently!"l transferred tolthe sludgeboilerernploying ordinary pipes and-pumping. equipment.. 4, l I v If desired, condensation of the vapors from the second Yvaporization step may beV omitted and the vapors transferred directly to the first Vrectifying column. it has been found-however that somewhatbetter control of the column operation isl obtained when the feed material is i. first condensed. dThe fractional distillation which. is ac- V complished inth'e first rectifying column is Varranged by Yseparation of low boiling point compounds has been obtained with reflux ratios within the rangerbetween l islamismo 1. Y Y Y Y The VTiCliV drawn oifthe bottom of the lirst rectication'gco'lumn vis transferred and subjected to aV second fractional distillation operation ,to separate it from high boiling vpoint compounds in the second rectifying column. This column is operated also according to known principles with suiiicient heat being applied to the TiCl4 boiler to provide proper amounts of TiCl4 vapor in the tower. As'in the first rectification column the reuii ratio may vary considerably but good results have been obtained with reflux ratios within theV range be-Y tween .lz to 1 and l0 to 1.

Continuous and economical operation of the rectiiicai tion columns does not produce perfectly separated high orflow boiling components. Employing'proper retiux ratios the low boiling fraction taken from the top of the first rectification column comprises tin chloride, silicon chloride,^and other compounds and gases whose boiling point is lower than that of TiCl4. In general and under conditions Where an optimum reflux ratio is em V ployed, theproportion of TiCl4 admixed with these low boiling point compounds will not be of large magnitude. Therefore with reasonable control of the retiux ratio and the column operating conditions, the'low boiling point vaporization from the top of the rst rectifying column may be'discarded without serious loss'of TiCl4.

The second rectification step produces purified titanium tetrachloride but operation of this column cannot be generally adjusted to provide aV sharp fractionation of manner that the still bottoms from the first and secondi evaporation steps are handled. A proportion ofthe high boiling `point compounds inY admixture with TiCl4 sho\1ld be continually removed fromthe material being trans-` i system. Y

i `a dry .residue is obtained. VA major part, preferably'SO to 80%-,V of the 'IiQli atthis stage is distilled over into Ytreatment but is preferred to carry this material :haelt-VV to the Yiirst evaporation stage so that anyy solids carriedi ferred from the bottom of the second rectifying column to the sludge boiler so that continual build up of Yhigh boil`r ing point components inthe over-all system is avoided. Bleeding oit a reasonable portion so that only a minor amountY of TiCl4 is discarded with the unwanted high boiling point componentswillbe found to provide adequate control of the high boiling point The sludge boiler, which is `eiect a recovery unit Afor separating'valuable TiCl4 from'the first `andsecond evaporation stepsk and from. the second'rectifyingl column, is operated to produce recovered TiCl4 and a solid dry residue which can be discardedor if desired maybe treat` l edto recovermetal values, such as vanadium and vzirconiumtherefrom. The'slurries entering the sludge boiler are'best handled in batches'and the temperature of the: f sludge boiler is heldV above the boiling point-loffl/'iCh Therecovered TiCl4 from the sludge boiler may be cornbined with'crude TiCl4 at any stageV prior `to chemical over in the sludge baking operation .will beseparated before the recovered `'TiCl4 vis adrnixedu'ith treating agent. If desired, and particularly if values are to be recovered from the residues, slurries from. the various steps may be treated separately forl recovery "of TiCl,

' which is recycled as described;

The integrated process as her'linbefore described 'pro-V vides a continuous method for producing titanium tetra.-v chloride of highest purity. TheV sequenceand arrangement of stepsl are important to insurey the required purity in the final product. Although the reasons for sor'ne effects encountered in suchV a'systemrare not'precisel'y 1 apparently is much morer eoient in precipitating vana-V dium salts and other contaminants when the crude 'I`iCl4` known'it has been discovered that final "l`iCl4V 'is' improved substantially over that obtained 'by heretofore known methods. The ychemical treating agent employed hasjtirst been` separated from Vresidual solids and snspendedmatter Vby a preliminary evaporation step, Moreover, under these conditions lsubstantialsaving 'may vbe i accomplished inasmuch as Van appreciably lower amount soV of treating agent will accomplish the same effect.

The arrangement and vsequence of the rectifying columns may be considered contrary to preferred'pr'esent practice employed in other industries. Separation Vof the low boiling compounds in the first step does not provide a clean feed to the second column as may be ordinarily considered 'more desirable. covered that titanium tetrachloride isre'xtremely sensitive to the presence of iinely divided solids which may build up and be formed at anystage of such a treatment procedure. Therefore, the disadvantage of a dirty distillation in the second rectifying column is more than compensated for by the advantage of taking the TiCl4 product off as a vapor in the final step and only a simple condensation is required to produce liquid TiCl4 for direct use.

We claim: Y l. Aprocess for the purification of crude titanium tetrachloride (TiCl4) which comprises evaporatingsaid crude TiCl4 to separate solid and non-volatile materials therefrom, precipitating' vanadium andY other impurities from said evaporated TiCl4 by means of a chemical treat-- ingv agent, evaporating said treated TiCl4 to separate non volatile precipitates therefrom, removing low boiling point impurities from'said treated and evaporated TiCliby a first fractional distillation and removing high boiling point pre*eip'itatingA vailnadiurn;and',other'impuritieslfrom` said content of the whole However, it hasbeen disevaporated TiCl4 by means of a chemical treating agent, evaporating a major portion of the treated TiCL, to separate a minor portion containing non-volatile precipitates therefrom, removing low boiling point impurities from said treated and evaporated TiCL, by a first fractional distillation Vand removing high boiling point impurities therefrom by a second fractional distillation, thereby to produce purified TiCl4, heating the minor portions separated in the first and second mentioned evaporation steps to recover TiCl4 therefrom and combining said recovered TiCl4 with crude T iCl., at a stage prior to chemical treatment.

3. A process for the purification of crude titanium tetrachloride (TiCl4) which comprises evaporating between 50% and 80% of said crude TiCl., to separate a minor portion thereof containing non-volatile solid materials, precipitating vanadium and other impurities from said evaporated TiCl.,l by means of a chemical treating agent, evaporating between 50% and 80% of the treated TiCL., to separate a minor portion containing non-volatile precipitates, removing W boiling point impurities from said treated and evaporated TiCl., by a iirst fractional distillation and removing high boiling point impurities therefrom by a second fractional distillation, thereby to produce purified TiCl4, combining the minor portions separated in the rst and second mentioned evaporation steps, heating said portions to recover TiCL4 therefrom and combining said recovered TiCl4 with crude TiCl., at a stage prior to chemical treatment.

4. A process for the purification of crude titanium tetrachloride (TiC14) which comprises evaporating a major portion of said crude TiCL, to separate a minon portion thereof containing non-volatile solid materials, precipitating vanadium and other impurities from said evaporated TiCL, by means of a chemical treating agent, evaporating a major portion of the treated TiCl, to separate a minor portion containing non-volatile precipitates, removing low boiling point impurities from said treated and evaporated TiCl.,l by a first fractional distillation and removing high boiling point impurities therefrom by a second fractional distillation, thereby to produce purified TiCl4, combining the minor portions separated in the first and second mentioned evaporation steps heating said portions to recover TiCl4 and to separate a dry residue therefrom, and combining said recovered TiCl4 with crude TiCl4, at a stage prior to chemical treatment.

5. A process for the purication of crude titanium tetrachloride (TiCl4) which comprises evaporating a major portion of said crude TiCL, to separate a minor portion thereof containing non-volatile solid materials,

precipitating vanadium and other impurities from said evaporated TiCl by means of a chemical treating agent, evaporating a major portion of the treated TiCl4 to separate a minor portion containing non-volatile precipitates, removing low boiling point impurities from said treated and evaporated T iCl4 by a rst fractional distillation and removing high boiling point impurities therefrom by a second fractional distillation, thereby to produce purified TiCl4, combining the minor portions separated in the first and second mentioned evaporation steps and a major portion of the high boiling point impurities removed in the second fractional distillation, heating said combined portions to recover TiCl4 therefrom and combining said recovered TiCL, with crude T iCl at a stage prior to chemical treatment.

6. A process for the purification of crude titanium tetrachloride (TiCl4) which comprises evaporating between 50% and 80% of said crude TiCl4 to separate a minor portion thereof containing non-volatile solid materials, precipitating vanadium and other impurities from said evaporated TiCl4 by means of a chemical treating agent, evaporating between 50 and 80% of the treated TiCl.,g to separate a minor portion containing non-Volatile precipitates, removing low boiling point impurities from said treated and evaporated TiCl4 by a first fractional distillation and removing high boiling point impurities therefrom by a second fractional distillation, thereby to produce purified TiCl4, combining the minor portions separated in the first and second mentioned evaporation steps and about of the high boiling point impurities removed in the second fractional distillation, heating said combined portions to recover TiCiitherefrom and combining said recovered TiCl., with crude TiCl4 at a stage prior to chemical treatment.

References Cited in the le of this patent UNITED STATES PATENTS 2,224,061 Pechukas July 7, 1942 2,289,328 Pechukas July 7, 1942 2,345,214 Pechukas Mar. 28, 1944 OTHER REFERENCES Chemical Engineers Handbook, by John H. Perry,

3rd ed. (1950), McGraw-Hill, sections 7 (Evaporation) and 9 (Distillation 

1. A PROCESS FOR THE PURIFICATION OF CRUDE TITANIUM TETRACHLORIDE (TICL4) WHICH COMPRISES EVAPORATING SAID CRUDE TICL4 TO SEPARATE SOLID AND NON-VOLATILE MATERIALS THEREFROM, PRECIPITATING VANADIUM AND OTHER IMPURITIES FROM SAID EVAPORATED TICL4 BY MEANS OF A CHEMICAL TREATING AGENT, EVAPORATING SAID TREATED TICL4 TO SEPARATE NONVOLATILE PRECIPITATES THEREFROM, REMOVING LOW BOILING POINT IMPURITIES FROM SAID TREATED AND EVAPORATED TICL4 BY A FIRST FRACTIONAL DISTILLATION AND REMOVING HIGH BOILING POINT IMPURITIES THEREFROM BY A SECOND FRACTIONAL DISTILLATION. THEREBY TO PRODUCE PURIFIED TICL4. 